ELM327
OBD-II to UART/BT/WiFi translator chip.
ELM327 is a chip by ELM Electronics that translates OBD-II protocols (K-Line, J1850, CAN) into simple ASCII "AT ..." / "01 ..." commands over UART. Nearly every consumer adapter (BT/WiFi/USB) is built around ELM327 v1.5 or v2.x. Clones: Chinese $5-15, genuine $50+.